azures and tincs are too agressive for groups/mixing in a home vivarium. If you really were set on mixing you should sell the 40 and get a much larger tank. You will be surprised how much a tank shrinks once the false bottom and backround is set up. As far as mixing species, luecomelas and galacts are the ones i think would be a safer bet than others as long as the tank had ample plants,hiding places,diffrent levels and places to set up territorys. And ofcourse any eggs that you find you must destroy(to prevent hybrids)